Aquastat Draft Fan Control

I was considering placing a low limit strap on aquastat to turn the draft fans off when the fire is going out.. I only have one aquastat to control the draft fan for the operating water temps. I would like to turn the fans off when the water temps drop out due to fire going out and no one at home to manually turn fans off.

I'd try emailing some of the advertising dealers here & ask them about a stack temp thermostat to do that. That way it would shut your fan down after the stack cools off but before the fan blows all the heat out of your boiler water.